It is sometimes desirable to process felled logs into lumber on site, thereby eliminating the need to transport the logs from the site to a sawmill and hence reducing fuel and labor costs. It is particularly desirable to do so if the logs are felled at a remote location and the lumber produced from such logs is to be used on site. Prior portable chain saw attachments designed to meet this need, sometimes referred to as "chain saw mills", have not proved entirely satisfactory.
Three similar chain saw attachments or mills are disclosed in Grube U.S. Pat. No. 4,244,104; Granberg et al. U.S. Pat. No. 4,070,757; and Hayden et al. U.S. Pat. No. 3,225,799. These patents each disclose a chain saw attachment having a frame or carriage attachable to the saw bar of the chain saw. Each attachment has parallel transverse frame elements supported by the log's upper surface. Such frame elements slide along the log's upper surface as the chain saw is fed lengthwise through the log to cut away a slab or section of preset thickness. These attachments operate on the premise that the transverse frame elements are supported on a perfectly flat, typically horizontal upper surface formed from a prior cut, except for a preliminary cut by which a portion of the log's rounded, outermost edge (sometimes referred to as "outer slab") is removed. Each preliminary cut is made by first nailing a board to the log's rounded outer surface to provide a flat, horizontal guide reference for the attachment. The log is then cut as just described, except that the frame elements are supported by the board instead of the log's upper surface.
The foregoing set-up procedure required for each outer slab cut is time-consuming, particularly since the board must be removed from the outer slab once the cut is completed. In addition, the foregoing attachments rely on the previous cut as a reference for the next cut and hence any inaccuracies, such as undulations, in a prior cut not only affect but can be compounded in later cuts. Further, at least a portion if not all the weight of the chain saw and attachment is exerted on the section or slab being cut, thereby causing an increased pinching force to be exerted on the saw chain during cutting and hence increased risk of chain binding, unless time-consuming precautions are taken. Also, such attachments are physically limited in their ability to process small diameter logs approaching six inches in diameter. Finally, the foregoing attachments are all relatively wide to accommodate large chain saws, making them unwieldy and bulky when used with smaller chain saws.
Other more complicated, heavier and therefore less portable "on site" log sawing devices are disclosed in Lovas et al. U.S. Pat. No. 4,332,084; Brown U.S. Pat. No. 4,122,604; and McManama U.S. Pat. No. 3,115,909. These devices have at least one feature in common with the foregoing chain saw attachments, namely, the use of the log's upper surface as a reference to support and guide the device during cutting. Thus, they have the same binding and, except for Lovas et al., inaccurate cutting, and preliminary set-up problems as the foregoing chain saw attachments. Also, they are even more limited in their capacity to cut small logs than the foregoing attachments.
The Lovas et al. apparatus uses a band mill instead of a chain saw. It is large and heavy and apparently requires more than one person to operate and handle it. It self-corrects for undulations in prior cuts to some degree but not altogether by supporting the apparatus on resilient rubber rollers in contact with the top of the log. The rollers average the vertical displacement of the frame over a greater distance and provide better weight distribution. A pendulum-type leveling means is provided as a visual guide for the operators during preliminary "outer slab" cuts, thereby eliminating the need to nail a board to the log's outer surface. However, such cuts are therefore subject to operator error, which results when the cutting plane of the saw chain is not kept perfectly horizontal.
The Brown and McManama devices also appear to be large, heavy machines which are difficult for one person to handle and operate. The McManama machine uses a band saw cutting mechanism, which is driven by an electric motor and hence requires a separate power source. The Brown machine, which appears to be specially designed to cut large logs, uses a chain saw type cutting means and includes power operated means for feeding the chain saw lengthwise through the log.
Accordingly, there is a need for an improved portable chain saw attachment that is simple, effective, accurate, efficient, capable of cutting small diameter logs and suitable for use by one person.